Device for determining a torque and/or a rotational angle of a shaft

ABSTRACT

A device for determining a torque and/or a rotational angle of a shaft, which has a circuit carrier, which is concentric to the shaft, and on which at least two current-conducting printed conductor sections are situated. The device additionally has one transducer element, which is concentric to the shaft and is rotatable in relation to the circuit carrier, having at least one first subarea made of electrically conductive material and at least one second subarea made of electrically nonconductive material. Upon application of a torque to the shaft, the transducer element rotates in relation to the circuit carrier, whereby an overlap area between the printed conductor sections and the first subarea(s) of the transducer element changes and thus a change in an inductance of the printed conductor sections occurs.

BACKGROUND INFORMATION

A measuring device for the contactless detection of a rotational angleand/or torque on a stationary or rotating shaft is described in GermanPatent No. DE 29 51 148, in which two bodies, which are concentric tothe shaft and are made of electrically conductive material, areprovided, one of which is connected rotationally fixed to the shaft andthe other of which is rotatable in relation thereto. A coil which isconcentric to the shaft is situated in direct proximity to the twobodies and the bodies contain cutouts whose shared overlap area changeswith increasing rotation angle occurring between the two bodies. In thismeasuring device, the fact is made use of that an alternating magneticfield originating from the coil generates stronger eddy currents in thetwo bodies the less the body adjacent to the coil is capable ofshielding the second body in partial areas or in its entirety.

Measuring devices or sensor systems of this type, which are based on thegeneration of eddy currents, are frequently also designated as eddycurrent sensors.

A further eddy current sensor system is also described, for example, inGerman Patent Application No. DE 10 2005 025 870.

SUMMARY OF THE INVENTION

The present invention provides a device for determining a torque and/ora rotational angle of a shaft, which has a circuit carrier concentric tothe shaft, on which at least two current-conducting printed conductorsections are situated. The device additionally has one transducerelement, which is concentric to the shaft and is rotatable relative tothe circuit carrier, having at least one first subarea made ofelectrically conductive material and having at least one second subareamade of electrically non-conductive material. Upon application of atorque to the shaft, the transducer element rotates in relation to thecircuit carrier, whereby an overlap area between the printed conductorsections and the first subarea(s) of the transducer element changes anda change in the inductance of the printed conductor sections thusoccurs.

In contrast to known sensor systems or measuring devices, the deviceaccording to the present invention having the circuit carrier and thetransducer element has only two components, which results in asignificant cost reduction. The fact that no further sensor elements arenecessary in addition to the printed conductor sections situated on thecircuit carrier and the transducer element also contributes tominimizing the cost expenditure. The device according to the presentinvention has a low sensitivity in relation to adjustment tolerances, sothat even slight tilting of the circuit carrier in relation to thetransducer element or a slight change in the spacing of the two elementsfrom one another still results in reliable measuring results. Inaddition, the device according to the present invention requires onlyvery little installation space, which represents a decisive advantage inmany applications.

According to one specific embodiment of the present invention, thetransducer element made of electrically conductive base material and thesecond subareas made of electrically nonconductive material are formedby openings, which are preferably implemented in the form of circularsectors or circular segments and are distributed uniformly over thetransducer element in the peripheral direction of the shaft.

According to an alternative specific embodiment of the presentinvention, the transducer element may also be made of electricallynonconductive base material, in this case, the first subareas made ofelectrically conductive material being formed by metal surfaces, whichare preferably implemented in the form of circular sectors or circularsegments and are distributed uniformly over the transducer element inthe peripheral direction of the shaft. The metal surfaces are preferablyimplemented as injection-molding-encapsulated metal inlay parts.

The printed conductor sections situated on the circuit carrier, whichact as antennas, may be implemented by printed conductors arranged onthe circuit carrier in spirals, which are preferably distributeduniformly over the circuit carrier in the peripheral direction of theshaft.

It is advantageous for the function of the device according to thepresent invention if the magnetic field generated by the printedconductor sections is oriented so it is focused on the transducerelement as much as possible. This focusing is achieved by printedconductors arranged in spirals, but may also be achieved by other planarconfigurations of the printed conductor sections without impairment ofthe function of the device according to the present invention.

The printed conductor sections acting as antennas form an openoscillating circuit, which oscillates at a predetermined frequency.According to an advantageous specific embodiment of the presentinvention, an analyzer circuit may also be provided on the circuitcarrier in addition to the printed conductor sections. This circuitanalyzes a change in the oscillation frequency of the oscillatingcircuit which is caused by the change in the inductance and determinesthe torque applied to the shaft and/or the rotational angle of the shaftas a function of the ascertained frequency change. The situatinganalyzer circuit on the circuit carrier contributes to both the costreduction and also the minimization of installation space.

According to a further advantageous specific embodiment of the presentinvention, the circuit carrier and/or the transducer element are coatedfor protection from environmental influences.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic perspective illustration of a first specificembodiment of the device according to the present invention fordetermining a torque and/or a rotational angle of a shaft.

FIG. 2 a shows a schematic illustration of the spatial configuration ofthe printed conductor sections in relation to the subareas of thetransducer element in a specific embodiment of the present inventionaccording to FIG. 1.

FIG. 2 b shows a schematic characteristic curve to represent the overlapof the printed conductor sections and the first subareas made ofelectrically conductive material of the transducer element as a functionof a rotation angle in a specific embodiment according to FIG. 1.

FIG. 3 shows a schematic top view of a second specific embodiment of thedevice according to the present invention.

DETAILED DESCRIPTION

In FIG. 1, a device according to the present invention for determining atorque and/or a rotational angle of a shaft (not shown) is shown in aschematic perspective view. Printed conductor sections 2 in the form ofprinted conductors arranged in spirals, which act as antennas, aresituated on a circuit carrier 1. In the specific embodiment shown, atotal of six printed conductor sections 2 are provided. However, it issufficient for the functional capability of the device according to thepresent invention if at least two printed conductor sections 2 areprovided. Fundamentally, 2*k printed conductor sections 2 with k=1, 2, 3. . . n are possible. The provision of more than two printed conductorsections 2 results in an increase of the resolution of the deviceaccording to the present invention and thus a more exact determinationof the torque and/or the rotational angle of the shaft. In addition, thepossibility results through the use of more than two printed conductorsections 2 of interconnecting printed conductor sections 2 into twogroups, and thus producing a redundancy, which results in an increase inthe reliability of the device according to the present invention.

A transducer element 3 has first subareas 4 made of electricallyconductive material and second subareas 5 made of electricallynonconductive material. According to the specific embodiment shown inFIG. 1, four first subareas 4 made of electrically conductive materialare provided, which are formed by metal surfaces, which are applied totransducer element 3, made of electrically nonconductive base material.The metal surfaces are distributed uniformly over transducer element 3in the peripheral direction of the shaft, so that second subareas 5 madeof electrically nonconductive material, which are required according tothe present invention, arise between first subareas 4 formed by themetal surfaces in each case. The metal surfaces are preferablyimplemented as injection-molding-encapsulated metal inlay parts.

According to the specific embodiment shown, four first subareas 4 madeof electrically conductive material and four second subareas 5 made ofelectrically nonconductive material are provided. However, it issufficient for the function of the device according to the presentinvention for the transducer element to have at least one first subarea4 made of electrically conductive material and one second subarea 5 madeof electrically nonconductive material. An obvious possible increase ofthe number of the subareas results in turn in an increased resolutionand thus a more precise determination of a torque and/or a rotationalangle of the shaft.

Alternatively to the specific embodiment shown, transducer element 3 mayalso be made of an electrically conductive base material, such as metal,and second subarea 5, made of electrically nonconductive material, maybe formed by simple cutouts or openings.

Both circuit carrier 1 and also transducer element 3 are situatedconcentrically to the shaft and are preferably implemented asdisc-shaped, for example, in the form of a circular disk. The metalsurfaces situated on transducer element 3 or the openings or cutoutsprovided in transducer element 3 are preferably distributed uniformly ontransducer element 3 in the peripheral direction of the shaft. Printedconductor sections 2 which are situated on circuit carrier 1 arepreferably also distributed uniformly over circuit carrier 1 in theperipheral direction of the shaft.

In order to achieve a rotation of transducer element 3 in relation tocircuit carrier 1 upon application of a torque to the shaft, a torsionbar (not shown) is preferably used, which connects a first subarea ofthe shaft to the second subarea of the shaft and twists upon applicationof a torque to the shaft. At least circuit carrier 1 or transducerelement 3 is fastened on the torsion bar. The particular other elementmay be fastened at a predetermined spacing to the first element on thetorsion bar as well, on the shaft itself, or also on a rotationallyfixed component situated in the area of the shaft, such as a housingpart. While the fastening of both elements, i.e., circuit carrier 1 andtransducer element 3, on the torsion bar or the shaft allows adetermination of the torque, fastening of one component on arotationally fixed component is used for determining the rotationalangle of the shaft.

Circuit carrier 1 has an opening 6, which is preferably adapted to theexternal shape of the shaft or the torsion bar, and which is used forfastening circuit carrier 1 on the shaft or the torsion bar. Circuitcarrier 1, which is produced from PCB or ceramic, for example, mayeither be fastened directly on the shaft or the torsion bar or, toincrease the mechanical stability and/or to simplify the installation,may also be fastened with the aid of a sleeve (not shown) on the shaftor the torsion bar.

An opening 7, which is adapted in its external shape to the shaft (notshown) or the torsion bar, is also provided in transducer element 3,which is used for fastening transducer element 3 on the shaft or thetorsion bar. Transducer element 3 may either be fastened directly on theshaft or the torsion bar or a sleeve may be used to increase themechanical stability and/or to simplify the installation.

If circuit carrier 1 or transducer element 3 is not fastened on theshaft or the torsion bar, but rather on a rotationally fixed component,such as a housing part, corresponding opening 6 or 7 may be dispensedwith and instead another suitable fastening device may be provided.

If a current is applied to printed conductor sections 2, which aresituated on circuit carrier 1, these sections act as antennas, which arepart of an open oscillating circuit, which oscillates at a predeterminedfrequency. If a torque is applied to the shaft, the relative position oftransducer element 3 to circuit carrier 1 changes and the overlap areabetween printed conductor sections 2 and first subareas 4 of thetransducer element, which are made of electrically conductive material,also changes. Because of self-induction, the inductance of printedconductor sections 2 thus also changes and therefore finally theoscillation frequency of the oscillating circuit changes. Upon maximumoverlap of a printed conductor section 2 with a first subarea 4 made ofelectrically conductive material, the inductance of the oscillatingcircuit is lowest and the oscillating frequency is thus highest. Thechange in the oscillating frequency of the oscillating circuit thusrepresents a measure of the rotational angle or the applied torque onthe shaft. This frequency change may be analyzed with the aid of ananalyzer circuit 8 and a torque and/or a rotational angle of the shaftmay be determined therefrom.

Analyzer circuit 8, which may be implemented by an ASIC and/or adiscrete circuit, for example, is advantageously situated on circuitcarrier 1 (FIG. 1). Analyzer circuit 8 may also be implemented as aseparate component, of course.

According to the specific embodiment shown in FIG. 1, printed conductorsections 2 are implemented as spiral printed conductors, but inalternative specific embodiments, they may also be implemented by otherplanar printed conductor configurations. Printed conductor sections 2are advantageously implemented so that they act as antennas, whichgenerate a magnetic field, which is oriented so it is focused ontransducer element 3 as much as possible. It is thus also advantageousif printed conductor sections 2 are implemented in regard to theirradial extension as extensively congruent with the radial extension offirst and second subsections 4 and 5 of transducer element 3.

The spatial configuration of individual subsections 4 and 5 oftransducer element 3 in relation to printed conductor sections 2 a, 2 b,and 2 c in the specific embodiment of the present invention according toFIG. 1 is shown in FIG. 2 a. It is to be noted here that this is solelya schematic illustration, which illustrates neither the realconfiguration of the individual elements nor their real implementation,but rather only shows the change in the overlap areas between printedconductor sections 2 and the first subareas of transducer element 3 as afunction of the rotation angle.

According to the specific embodiment shown in FIG. 1, four firstsubareas 4 in the form of metal surfaces and six printed conductorsections 2 a, 2 b, and 2 c, which are situated on circuit carrier 1, areprovided on transducer element 3 (not shown in FIG. 2 a), which are eachonly indicated in FIG. 2 a by corresponding circular sectors. Accordingto the illustration in FIG. 2 a, circuit carrier 1 has a circular shape,printed conductor sections 2 a, 2 b, and 2 c and first subareas 4 oftransducer element 3 each covering a peripheral angle of 45° and beingdistributed uniformly over circuit carrier 1 or transducer element 3 inthe peripheral direction. A spacing angle of 15° results in each casebetween two adjacent printed conductor sections 2.

A schematic characteristic curve is shown in FIG. 2 b, which illustratesa degree of the overlap between printed conductor sections 2 a, 2 b, and2 c and first subareas 4 of transducer element 3 as a function of therotational angle of transducer element 3 in relation to circuit carrier1. The characteristic curve for printed conductor sections 2 a isdesignated by reference numeral 20 a, the characteristic curve forprinted conductor sections 2 b by reference numeral 20 b, and thecharacteristic curve for printed conductor sections 2 c by referencenumeral 20 c. The assumed rotational direction of transducer element 3and thus first subareas 4 is indicated in FIG. 2 a by an arrow 10. Thus,for example, at a rotational angle of 0°, i.e., in the starting positionshown in FIG. 2 a, an overlap of 1 results for printed conductorsections 2 b, i.e., a complete overlap. In contrast, printed conductorsections 2 a and 2 c only have an overlap of ⅓, i.e., 15°. At arotational angle of 75°, for example, an overlap of ⅔ results forprinted conductor sections 2 b and 2 c, while in contrast printedconductor sections 2 a have no overlap.

A top view of a device according to the present invention according to asecond specific embodiment is shown in FIG. 3. Transducer element 3 isshown as slightly transparent, so that the part of circuit carrier 1lying underneath is also recognizable. In addition to printed conductorsections 2, further printed conductor structures 30 are provided on thecircuit carrier, which also act as antennas, and an additional metalsurface is provided on transducer element 3, which forms a furthersubarea 31 of transducer element 3 made of electrically conductivematerial. Further printed conductor structures 30 and further subarea 31fundamentally operate according to the same principle as printedconductor sections 2 in interaction with first subareas 4. It is alsosufficient to provide at least two further printed conductor sections 30on circuit carrier 1 and at least one further subarea 31 made ofelectrically conductive material and one further subarea made ofelectrically nonconductive material on the transducer element. Forexample, with the aid of further printed conductor structures 30 and thefurther subareas of transducer element 3, an index function may beimplemented, which may be used for the plausibility check of the torqueand/or rotational angle value determined with the aid of printedconductor sections 2.

An index function of this type acquires particular significance for thecase in which the device is designed redundantly. Redundant means that,of the 2*k printed conductor sections acting as antennas, k printedconductor sections, i.e., half of them, are each used for determiningthe torque and/or the rotational angle of the shaft. In this way, twoindependent redundant signals are obtained, which contributes toincreasing the reliability and thus the security of the device. Invarious applications, redundancy is also absolutely required, which isto be implemented cost-effectively in this manner. However, themeasuring range is halved from 360° to 180° by this procedure.

This reduction of the measuring range may also be compensated for byfurther printed conductor structures 30, which also act as antennas,because it may be ascertained with the aid of these structures in whichsubarea the value of the rotational angle must lie. If, as shown in FIG.3, four further printed conductor structures 30 are provided, an indexfunction results therefrom, which divides the measuring range into foursubsections from 0° to 90°, 90° to 180°, 180° to 270°, and 270° to 360°.With only two printed conductor structures 30, a division into twosubareas from 0° to 180° and 180° to 360° would result correspondingly.

If the device according to the present invention is used for determiningthe rotational angle of a shaft, i.e., circuit carrier 1 or transducerelement 3 is fastened on a rotationally-fixed component situated in thearea of the shaft, rotational angles of 360° and more may also occur.The index function may also be advantageously employed by using it as atype of counter, which shows the number of the revolutions.

In addition, a plug 32 is provided in FIG. 3, via which printedconductor sections 2 and/or structures 30 and/or analyzer circuit 8 areelectrically contacted. A plug 32 of this type is usable for contactingthe individual components independently of the concrete specificembodiment of the device according to the present invention, of course.

Both circuit carrier 1 and also transducer element 3 are advantageouslyhoused in a common housing. The components may be partially orcompletely coated, e.g., with the aid of lacquer or polymer coatings,for protection from environmental influences.

The device according to the present invention is capable in particularof determining a torque and/or a rotational angle of a steering columnin a motor vehicle.

1. A device for determining at least one of a torque and a rotationalangle of a shaft, comprising: a circuit carrier, which is concentric tothe shaft, and on which at least two current-conducting printedconductor sections are situated; and a transducer element, which isconcentric to the shaft and is rotatable in relation to the circuitcarrier, having at least one first subarea made of electricallyconductive material and at least one second subarea made of electricallynonconductive material, wherein, upon application of a torque to theshaft, the transducer element rotates in relation to the circuitcarrier, wherein an overlap area between the printed conductor sectionsand the first subarea of the transducer element changes and a change inan inductance of the printed conductor sections occurs.
 2. The deviceaccording to claim 1, wherein the circuit carrier and the transducerelement have a disk-shaped design.
 3. The device according to claim 1,wherein the transducer element is made of electrically conductive basematerial and cutouts in the form of sectors or segments are provided,which form the second subarea and are distributed uniformly over thetransducer element in a peripheral direction of the shaft.
 4. The deviceaccording to claim 1, wherein the transducer element is made ofelectrically nonconductive base material and metal surfaces in the formof sectors or segments are provided, which form the first subarea andare preferably distributed uniformly over the transducer element in aperipheral direction of the shaft.
 5. The device according to claim 4,wherein the metal surfaces are injection-molding-encapsulated metalinlay parts.
 6. The device according to claim 1, wherein the printedconductor sections are formed by printed conductors arranged in spiralson the circuit carrier, which are distributed uniformly over the circuitcarrier in a peripheral direction of the shaft.
 7. The device accordingto claim 1, further comprising an analyzer circuit situated on thecircuit carrier, for analyzing a change, which is caused by the changein the inductance, in an oscillation frequency of an oscillating circuitformed from the printed conductor sections.
 8. The device according toclaim 1, wherein the circuit carrier and the transducer element arehoused in a common housing and the printed conductor sections areelectrically contacted via a plug.
 9. The device according to claim 1,wherein at least one of the circuit carrier and the transducer elementis coated for protection from environmental influences.